1. Field of the Invention
The present invention relates to a treatment system for performing a treatment for planar workpieces such as semiconductor substrates and LCD substrates and a treatment apparatus for the same.
2. Description of the Related Art
In semiconductor production process and LCD production process, a container called a carrier, cassette, or the like is used to transfer a plurality of workpieces (such as semiconductor substrates and LCD substrates) at a time so as to improve productivity.
For example, in a semiconductor production plant, a plurality of (for example, 25) semiconductor wafers which have been lithography treated are contained in a carrier. The carrier is transferred by a transfer robot to a heat treatment apparatus. In a conventional heat treatment apparatus, semiconductor wafers are transferred from a carrier to a wafer boat. A large number of wafers (for example, 100 wafers) are placed on the wafer boat at a time. The wafers on the wafer boat are loaded in a furnace. In the furnace, the wafers are oxidized, diffused, or heat-treated (for example, by CVD method). The wafers which have been heat-treated are transferred from the wafer boat to a carrier. Thereafter, the carrier is transferred to the transfer robot.
Thus, in this heat treatment apparatus, 100 wafers (which are contained in a total of four carriers) are heat-treated at a time. Since the transfer robot transfers one or two carriers at a time, however, carriers which contain wafers which have not been heat-treated are stored on a shelf disposed in the heat treatment apparatus. In a heat treatment system having a plurality of heat treatment apparatuses, a carrier storage chamber which is called a carrier stocker or simply called stocker is additionally provided. This carrier storage chamber stores several dozens of carriers.
Conventionally, clean air is blown to carriers stored on the carrier storage shelf or in the carrier storage chamber so as to prevent particles from adhering to the wafers. However, in the vicinity of the carrier storage shelf and in the carrier storage chamber, molecules of O.sub.2 and H.sub.2 O in air cause the surfaces of wafers to be oxidized, thereby forming unnecessary natural oxide films. For example, in CVD process for depositing a metal layer, if a natural oxide film is formed on a surface of a wafer, the film forming characteristics of metal layers deposited thereon adversely fluctuate. Thus, it is undesirable to allow carriers or wafers which are being temporarily stored to be oxidized. Since carriers may be stored in the carrier storage chamber for long periods, such natural oxide films are very likely to form.